Field of Disclosure
The present disclosure relates generally to a technique of acquiring a burst of TDMA signals in a reliable manner, while maintaining a low signal to noise ratio.
Description of Related Art
The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Time-division-multiple-access (TDMA) schemes have been widely used in very small aperture terminal (VSAT) satellite systems. In such VSAT systems, a number of remote terminals utilize the TDMA channel to share satellite resources in time. The ever increasing need for communications on the move (COTM) applications in satellite communication systems enforces the system's operating signal to noise ratio (SNR) to be in the sub-zero decibel (dB) region. For instance, in some VSAT applications, TDMA receivers are required to operate at a channel SNR as low as −10 dB.
Generally, burst detection methods rely on a correlation between the received burst or frame signal, which usually begins with a sequence of a known data pattern (called a preamble) followed by payload data, and a local copy of the known data pattern. Very often, Constant False Alarm Ratio (CFAR) detection techniques are employed for reliable burst detection when using such a correlation based method. However, such a correlation based detection method may disadvantageously require carrier synchronization between the transmitter and the receiver. For instance, in the case of having a central hub and remote terminals, if the terminals are not synchronized to the hub, the correlation performance may degrade which in turn may adversely affect the signal detection performance.
In order to detect TDMA bursts at low SNR, one option is to increase the preamble length. However, in order to reduce the correlation degradation due to frequency error, a short data sequence may be preferred. Such conflicting requirements may prevent the use of the above described correlation based burst detection methods in detecting signal bursts at very low SNR.